1. Field of the Invention
This invention relates to a method of converting a picture signal, an apparatus for converting a picture signal, and an apparatus for recording and reproducing a picture signal. In addition, this invention relates to a method of encoding a picture signal, a method of decoding a picture signal, an apparatus for encoding a picture signal, and an apparatus for decoding a picture signal.
2. Description of the Related Art
Some digital VTR's (video tape recorders) handle digital component video signals (digital Y, Cr, and Cb signals) which are derived from analog component video signals (analog Y, Cr, and Cb signals) through an analog-to-digital conversion process. Here, the Y signals mean luminance signals. In addition, the Cr signals mean R-Y signals (first color difference signals) while the Cb signals mean B-Y signals (second color difference signals). Specifically, during the analog-to-digital conversion process, the analog Y, Cr, and Cb signals are sampled at given sampling frequencies respectively, and then the samples of the analog Y, Cr, and Cb signals are digitized.
There are the DV standards (the DVC standards) for home-use digital VTR's. Here, "DV" is short for digital video, and "DVC" is short for a digital video cassette. According to the DV standards, the ratio among the sampling frequencies for the respective analog Y, Cr, and Cb signals is "4:1:1".
Digital picture signals for DVD's (digital versatile discs) and CS digital broadcasting conform to the MPEG2 (Moving Picture Experts Group 2) standards. According to the MPEG2 standards, the ratio among the sampling frequencies for respective analog Y, Cr, and Cb signals is "4:2:0 (4:0:2)". In an example of the 4:2:0 signal format, horizontal scanning lines related to a sampling frequency ratio of "4:2:0" alternate with horizontal scanning lines related to a sampling frequency ratio of "4:2:0". Such a signal format is denoted by "4:2:0" for convenience.
Any simple methods and apparatuses for converting 4:1:1 picture signals into 4:2:0 picture signals are unknown. In addition, any simple methods and apparatuses for converting 4:2:0 picture signals into 4:1:1 picture signals are unknown. Japanese published unexamined patent application 8-46519 discloses a specification conversion circuit which operates to convert a 4:2:2 picture signal into a 4:2:0 picture signal.